3. Therapy Modes and Controls
3.9 Lung Parameters
The advanced measurement system of Trilogy EV300 estimates lung compliance, airway resistance, AutoPEEP and plateau pressure during normal mechanical ventilation without requiring a static maneuver. It is unnecessary to perform an inspiratory hold to assess the plateau pressure and other lung parameters.
3.9.1 Dyn R
Airway resistance is the opposition to the motion of gas within the airways. In the Measured and Calculated Parameters window, this value is Dyn R (dynamic resistance). Dyn R is an estimate of the airway resistance in cmH20/L/s and is computed on a breath-to-breath basis without requiring a static maneuver.
It is updated at the end of exhalation of every mandatory or assisted (timed cycled) breath, and is displayed as the average over the last three mandatory or assisted breaths. It is corrected to body temperature and pressure saturated (BTPS) conditions.
This value appears in the displayed parameters pane when the therapy mode is A/C-PC, A/C-VC, SIMV-PC, or SIMV-VC and the circuit type is passive, active flow, or dual limb.
To calculate Dyn R, at the end of inhalation, Trilogy EV300 estimates the airway resistance by computing the ratio between the driving pressure from within the lung to the air flow. The flow term is corrected to take into account the contributions of the following:
• Intrinsic PEEP, by subtracting the expiratory flow at the end of exhalation
• The elastic recoil of the lungs, by adding the tidal volume divided by the respiratory time constant,
τ
. (Respiratory time constant is the airway resistance times the summed compliance of the lung and chest wall)Trilogy EV300 calculates Dyn R using the following formula:
Where:
• PIP is the peak inspiratory pressure (pressure at the end of inhalation)
• PEEPe is the extrinsic pressure (pressure applied by the ventilator) at the end of the breath
• Vt is the tidal volume
• Qp (t=EOE) is the patient flow at the end of the exhalation (EOE)
• Qp (t=EOI) is the patient flow at the end of inhalation(EOI)
To understand the calculations adopted to compute Dyn R, note that the above equation can be rewritten as the classic equation for airway resistance:
That is to say, pressure across the resistance equal to resistance times flow, where:
• PEEPi = —DynR*Qp(EOE) this value is the intrinsic PEEP or AutoPEEP (See “3.6.4 AutoPEEP”)
• PEEPe + PEEPi is the total pressure (extrinsic plus intrinsic) at the end of the breath
3.9.2 Dyn C
Lung Compliance is the ratio between the tidal volume and the changes in pressure. In the Measured and Calculated Parameters window, this value is Dyn C (dynamic compliance). Dyn C is an estimate of the compliance of the pulmonary system (lung and chest wall) in milliliters per cmH2O, computed on a breath-to-breath basis without requiring a static maneuver.
It is updated at the end of exhalation of every mandatory or assisted breath (time cycled), and is displayed as the average over the last three mandatory or assisted breaths. It is corrected to body temperature and pressure saturated (BTPS) conditions.
This value appears in the displayed parameters pane when the therapy mode is A/C-PC, A/C-VC, SIMV-PC, or SIMV-VC and the circuit type is passive, active flow, or dual limb.
To calculate Dyn C, the compliance of the respiratory system can be derived from the measurement of plateau pressure, Dyn Pplat using the relationship between the tidal volume, Vt, and the difference between the Dyn Pplat and PEEP.
Trilogy EV300 calculates Dyn C using the following formula:
Where:
• PEEP is the total pressure (intrinsic plus extrinsic) at the start of the breath (PEEP= PEEP_i+ PEEP_e)
• Vt is the tidal volume
Note that the compliance is related to the airway resistance by the respiratory time constant,
τ
, by therelationship described above.
3.9.3 Dyn Pplat
Plateau pressure is the maximum pressure applied to small airways and alveoli during positive-pressure mechanical ventilation. In the Measured and Calculated Parameters window, this value is Dyn Pplat. Dyn Pplat is an estimate of the maximum alveolar pressure during inspiration in cmH20, computed on a breath-to-breath basis without requiring a static maneuver. It is compensated for Auto-PEEP. This value is updated at the end of exhalation of every mandatory or assisted (timed cycled) breath.
This value appears in the displayed parameters pane when the therapy mode is A/C-PC, A/C-VC, SIMV-PC, or SIMV-VC and the circuit type is passive, active flow, or dual limb.
Having already estimated the compliance (Dyn R and Dyn C above), Trilogy EV300 calculates Dyn Pplat as follows:
Where:
• Vt is the tidal volume
• Dyn C is dynamic compliance
• PEEP is the total pressure (intrinsic plus extrinsic) at the start of the breath (PEEP= PEEP_i+ PEEP_e)
• PEEPi = —DynR*Qp (EOE) this value is the intrinsic PEEP or AutoPEEP
3.9.4 AutoPEEP
Intrinsic PEEP, PEEPi, is the resistive pressure at the end of exhalation (EOE), that occurs when a new breath is initiated before the previous breath is completed. In the Measured and Calculated Parameters window, this value is AutoPEEP. AutoPEEP is an estimate of the any pressure (above PEEP) that exists in the patient airway at the end of exhalation This value is updated at the end of exhalation of every mandatory or assisted (timed-cycled) breath.
This value appears in the displayed parameters pane when the therapy mode is A/C-PC, A/C-VC, SIMV-PC, or SIMV-VC and the circuit type is passive, active flow, or dual limb.
Trilogy EV300 calculates AutoPEEP using the following formula:
Where:
• Dyn R is the dynamic resistance (explained in “3.6.1 Dyn R”)
• Qp (t=EOE) is the patient flow at the end of the exhalation (EOE)
4.1 Overview
To set up Trilogy EV300, follow the steps shown below. See the accompanying section for instructions.
1. “Placement”
2. “Connecting AC Power”
3. “Installing Filters”
4. “Connecting a Circuit”
5. “Connecting External Patient Monitors” (optional step) 6. “Adding Oxygen”
7. “Starting Trilogy EV300”
4.2 Placement
Place Trilogy EV300 on a stable, flat, hard surface. Air must flow freely into the air inlet port and out of the exhalation valve. Do not block the air vents with items such as bedding or curtains. Do not place Trilogy EV300 near any heating or cooling equipment or air supplies such as forced air vents, radiators, or air conditioners. Be sure the USB and detachable battery panel doors remain closed when not in use.
If the device has been stored outside the normal operating temperature stated in “Technical Data,” be sure the device reaches operating temperature before starting.
See the “EMC Information” section for guidance on possible electromagnetic interference.
4.3 Connecting AC Power
Use the AC cord provided to connect AC power. Verify Trilogy EV300 is using AC power, indicated by the green LED light next to the On/Off (Standby) button.
To use another power source, such as a battery, see the “Power Management” section.